1. Field of the Invention
The present invention relates to a motion detector for use in a luminance/chroma separator which separates a composite video signal to provide a luminance signal and a chroma signal, for example.
2. Description of the Related Art
Television receivers include a luminance/chroma separator to separate a composite video signal to provide a luminance signal and a chroma signal.
FIG. 1 of the accompanying drawings shows in block form a circuit arrangement of a television receiver. As shown in FIG. 1, a composite video signal applied to an input terminal 1 is converted by an analog-to-digital (A/D) converter 2 to a digital composite video signal. The digital composite video signal from the A/D converter 2 is supplied to a luminance/chroma (Y/C) separator 3. The luminance/chroma separator 3 detects and separates the digital composite video signal supplied thereto by using a correlation between adjacent horizontal lines of each field and a correlation between the frames to provide a luminance signal Y and a chroma signal C.
The digital luminance signal Y from the luminance/chroma separator 3 is converted by a digital-to-analog (D/A) converter 4 to an analog luminance signal and supplied to a matrix circuit 5. The digital chroma signal C from the luminance/chroma separator 3 is converted by a D/A converter 6 to an analog chroma signal and supplied to a color demodulator 7. The color demodulator 7 demodulates the analog chroma signal supplied thereto to provide color difference signals R-Y and B-Y. The color difference signals R-Y, B-Y from the color demodulator 7 are supplied to the matrix circuit 5. The matrix circuit 5 processes the luminance signal Y and the color difference signals R-Y, B-Y supplied thereto to provide three primary color signals R (red), G (green), B (blue) and supplies these color primary color signals R, G, B to a cathode ray tube (CRT) 8 which then displays a color image on its picture screen.
The luminance/chroma separator used in the television receiver will be described more fully with reference to FIG. 2. In FIG. 2, reference symbol 10 generally depicts a luminance/chroma separator. The luminance/chroma separator 10 is what might be called a motion adaptive type luminance/chroma separator for changing the processing of an extracted chroma signal in accordance with a motion of a video signal. In the motion adaptive type luminance/chroma separator 10, as shown in FIG. 2, a composite video signal applied to an input terminal 11 is supplied to an intrafield chroma component extractor 12. The intrafield chroma component extractor 12 extracts a chroma component by using a correlation between adjacent lines of a video signal of each field, and supplies an extracted chroma component through a coefficient multiplier (x k) 13 to an adder 14. The coefficient multiplier 13 multiplies the chroma component with a coefficient k (0.ltoreq.k.ltoreq.1) supplied thereto from a motion detector 20 which will be described later on.
Also, the composite video signal applied to the input terminal 11 is supplied to an interframe chroma component extractor 15. The interframe chroma component extractor 15 extracts a chroma component by using a correlation between video signals of the same line of the frames, and supplies an extracted chroma component to the adder 14 through a coefficient multiplier (x (l-k)) 16. The coefficient multiplier 16 multiplies the chroma component with a coefficient (l-k) supplied thereto from the motion detector 20.
The adder 14 adds the chroma components extracted by the chroma component extractors 12, 15 and supplies an added chroma component to a subtracter 17. The subtracter 17 is supplied with the composite video signal from the input terminal 11 and subtracts the chroma component outputted from the adder 14 from this composite video signal. Then, the subtracter 17 supplies a subtracted signal to an output terminal 18 as the luminance signal Y and also supplies the chroma component outputted thereto from the adder 14 to an output terminal 19 as the chroma signal C.
The composite video signal applied to the input terminal 11 is supplied to the motion detector 20, and the motion detector 20 detects a motion of a picture represented by the composite video signal. A circuit arrangement of the motion detector 20 will be described with reference to FIG. 3, for example. As shown in FIG. 3, a composite video signal applied to an input terminal 21 is supplied to a one frame period delay circuit 22, and a subtracter 23 subtracts a signal delayed by the one frame period delay circuit 22 and the composite video signal directly supplied thereto from each other. When a difference between the frames of the video signal is obtained by the subtracter 23, if a picture represented by the video signal has a motion, then the subtracter 23 outputs a signal of the level corresponding to a motion amount as a frame difference signal. The frame difference signal is supplied to a low-pass filter (LPF) 24. The low-pass filter 24 eliminates a color subcarrier frequency band (i.e., frequency band near 3.58 MHz) and supplies its output to a motion coefficient generator 25. The motion coefficient generator 25 judges the motion amount on the basis of the frame difference signal supplied thereto, and generates coefficients k and (l-k) corresponding to the judged motion amount. Then, the motion coefficient generator 25 supplies the coefficients k and (l-k) through output terminals 26, 27 to the coefficient multipliers 13, 16 (see FIG. 2).
The coefficient k corresponding to the motion amount is set to 0 (k=0) if it is determined that a picture has no motion at all (i.e., a still image), and the coefficient k is set to 1 (k=1) if it is determined that a picture has a large motion amount. The coefficient k is set to an intermediate value ranging from 0 to 1 in response to a motion amount obtained at that time when a picture has an intermediate motion amount.
The coefficients k are changed as described above. Therefore, if a picture has no motion amount and the coefficient k is 0 (k=0), then the coefficient 0 is set to the coefficient multiplier 13 and the chroma component extracted by the intrafield chroma component extractor 12 is not supplied to the adder 14 at all. Also, the coefficient 1 is set to the coefficient multiplier 16 and the chroma component extracted by the interframe chroma component extractor 15 is supplied to the adder 14 as it is. Accordingly, under the condition that the picture has no motion amount, the adder 14 outputs only the chroma component extracted by the interframe chroma component extractor 15 so that the chroma component used by the subtracter 17 to generate the luminance signal and the chroma signal output from the output terminal 19 are only the chroma component extracted on the basis of the correlation between the frames of the video signal.
Conversely, if a picture has a large motion amount and the coefficient k is set to 1 (k=1), then the coefficient 1 is set to the coefficient multiplier 14 and the chroma component extracted by the intrafield chroma component extractor 12 is supplied to the adder 14 as it is. Also, the chroma component extracted by the interframe chroma component extractor 15 is not supplied to the adder 14 at all. Accordingly, under the condition that a picture has a large motion amount, the adder 14 outputs only the chroma component extracted on the basis of the correlation within one field of the video signal, and the chroma component used by the subtracter 17 to generate the luminance signal and the chroma signal output from the output terminal 18 are only the chroma component extracted from the video signal of one field.
If it is determined that a picture has a small amount of motion, then the coefficient k is set to the intermediate value ranging from 1 to 0 so that the adder 14 adds the chroma component extracted by the intrafield chroma component extractor 12 and the chroma component extracted by the interframe chroma component extractor 15 with a proper adding ratio. Therefore, the chroma component used to generate the luminance signal and the outputted chroma signal become such ones that result from mixing the two chroma components with a proper mixing ratio.
The luminance signal Y and the chroma signal C separated from the composite video signal are output from the output terminals 18, 19, whereby the luminance signal and the chroma signal are separated satisfactorily in response to the motion of the picture represented by the video signal. Specifically, if a picture has a small amount of motion, then the processing that mainly uses the chroma component extracted on the basis of the correlation of pictures provided between the frames is carried out and the separation processing with high accuracy suitable for a still image is carried out. If a picture has a large motion amount, then the processing that mainly uses the chroma component in which the extracting processing is completed at every field is carried out and the satisfactory separation processing following the motion of the picture is carried out.
Alternatively, the motion detector shown in FIG. 3 may be replaced with a motion detector shown in FIG. 4. As shown in FIG. 4, a composite video signal applied to an input terminal 31 is supplied to a luminance component extracting comb filter 32. In the comb filter 32, an adder 32b adds a signal delayed by a delay circuit 32a by 1H (one horizontal line) period and a signal, which is not delayed by the delay circuit 3a, to provide a luminance component. The luminance component obtained by the comb filter 32 is supplied to a subtracter 33. The composite video signal applied to the input terminal 31 is also delayed by a delay circuit 34 by a one frame period, and the delayed composite video signal is supplied to a luminance component extracting comb filter 35. Also, in the luminance component extracting comb filter 35, an adder 35b adds a signal delayed by a delay circuit 35a by 1H period and a signal, which is not delayed by the delay circuit 35a, to provide a luminance component. The luminance component obtained by the comb filter 35 is supplied to the subtracter 33.
The subtracter 33 subtracts the luminance component of the video signal preceding one frame from the luminance component of the video signal of the present frame to provide a difference signal, and supplies the difference signal to the low-pass filter 24. A rest of the circuit arrangement shown in FIG. 4 is the same as that of the motion detector shown in FIG. 3. Specifically, the low-pass filter 24 eliminates the frequency band of the color subcarrier. The output of the low-pass filter 24 is supplied to the coefficient generator 25 which generates the coefficients K and (l-k) corresponding to the judged motion amounts. Then, the coefficients k and (l-k) are supplied from the output terminals 26, 27 to the coefficient multipliers 13, 16 (see FIG. 2).
The motion detector shown in FIG. 4 can generate the coefficient k and (l-k) corresponding to the motion amounts similar to the motion detector shown in FIG. 3.
Although the motion detector shown in FIG. 3 includes the low-pass filter 24 to eliminate the chroma component contained in the frequency band of the color subcarrier from the composite video signal, if the chroma component is eliminated by the low-pass filter 24, then a high band component of the luminance component contained in the component video signal is also eliminated by the low-pass filter 24. If the high band component (i.e., information representing a small picture pattern portion of an image) of the luminance component is eliminated, then only the low frequency component (i.e., information representing a comparatively large picture pattern of an image) is supplied to the motion coefficient generator 25 as a motion signal and a high frequency motion component is not supplied thereto. Therefore, a moving picture having a small picture pattern (e.g., image representing that cross stripes are being moved) cannot be detected as a motion of a video signal.
If the moving picture with a small picture pattern were not detected, then the above-mentioned motion adaptive type luminance/chroma separator would separate the composite video signal by using the chroma component extracted by the interframe chroma extractor 15 to provide the luminance signal and the chroma signal even though an image is a moving picture, thereby deteriorating the picture quality.
On the other hand, since the motion detector shown in FIG. 4 carries out the motion detection after the luminance component extracting comb filters 32, 34 extracted only the luminance component, the low-pass filter 24 may be removed. However, in a picture in which a color is changed in the vertical direction, a chroma component is leaked to the outputs of the comb filters 32, 34 and therefore the low-pass filter 24 is also required. Thus, similar to the motion detector shown in FIG. 3, the low-pass filter 24 eliminates the high band component of the luminance signal and the motion detector shown in FIG. 4 cannot detect a moving image with a small picture pattern as a motion of a video signal.
While the motion detector required when the composite video signal is separated to provide the luminance signal and the chroma signal has been described so far, a motion detector required to effect other video signal processing encounters with similar shortcomings and disadvantages.